1. Field
The present invention relates to secure authentication and more particularly to authentication of limited resource devices.
2. Background
Electronic authentication typically involves some form of digital signature or message authentication code based on public-key (asymmetric-key) or symmetric-key cryptographic methods, respectively. Public-key and symmetric-key methods have different characteristics, making them applicable in different situations. Generally speaking, public-key systems have great advantages in terms of key management and distribution, but are computationally difficult and the digital signatures generated tend to be large. Symmetric-key methods, while very efficient and producing small outputs, have the drawback that they cannot be securely used with multiple verifying parties simultaneously.
Most small authentication tokens have been forced, by both limited computational resources and the need for small outputs, to use symmetric-key cryptography. In turn, this means that the token can only be used for authentication with only one verifying party. For example, two different entities may issue compatible tokens with different symmetric keys, but they cannot be combined into one token because that would necessitate sharing the symmetric key and the parties may not trust each other. With a recent announcement that U.S. banks will implement two-factor authentication methods, users may have to carry around multiple authentication tokens everywhere they go.
Authentication methods based on public-key systems have been proposed, but one drawback is that they demand greater computational resources than is available on many tokens. That is, tokens tend to be inexpensive and/or have limited processing resources. Adding more powerful processors to such tokens not only increases costs but also leads to having shorter battery lifetimes. Another drawback of using a public-key system is that the longer size of digital signatures makes it cumbersome to implement in comparison to typing or reading out a short sequence of digits.
Another type of authentication system uses trusted third parties to mediate the authentication. An example of such a system is MIT's Kerberos. However, reliance on a trusted third party is a deal-breaker for many institutions, such as banks, since it adds another point where security may be compromised.
Therefore, there is a need for a way to combine the advantages of public-key and symmetric-key systems to provide small and efficient digital signatures so that a single token can be used with multiple verifiers.